The invention relates to an extraction tower for the counter-current leaching of comminuted vegetable matter, such as sugar beet cossettes, or crushed sugar cane. As disclosed in our above mentioned earlier U.S. Patent, such towers include a housing and a central shaft rotatably supported in the housing. The conveying means for moving the comminuted vegetable matter axially from the bottom to the top of the tower include a central drive shaft having secured thereto conveying wings providing a screw type transport action. The conveying means further include baffle elements secured to the inner wall of the tower housing. As disclosed in our earlier patent, the baffle conveying elements and/or the wing type conveying elements may be rotatable about their longitudinal axis, at least through a certain angular range. The conveying baffle elements project into the spaces between adjacent wings of the conveyor shaft, whereby the wings and the baffles cooperate in conveying the material upwardly through the tower against the downwardly flowing extraction liquid.
As disclosed in our above mentioned patent, at least some of the conveying elements are provided with pressure or bending responsive sensors, such as strain gauges or the like, generating a respective control signal which is used for changing the composition and/or quantity of the supplied material as it is conveyed through the tower. This control is accomplished by adjusting the angular position of any one of the conveying elements and/or for regulating the drive motor of the central conveying shaft.
The teaching disclosed in our above mentioned U.S. Pat. No. 3,953,224 is based on the recognition that the load which is measured at any member participating in the conveying, permits a conclusion with regard to the consistency of the materials being conveyed at the point of measurement. This conclusion may be made regardless where the measuring takes place in the tower, for example, at a stop member, a baffle plate, a wing, and/or a worm turn or screw turn of the central conveying shaft, because the load responsive sensor or pick-up which may respond to pressure or bending, provides a signal which will be larger when the material being conveyed is densely packed and the signal will be smaller when the material is not so densely packed.
The ever increasing dimensions of extraction towers involve a substantial number of technological advantages. However, at the same time the distribution of the vegetable matter, as it is moved through the tower, may not necessarily be homogeneous throughout the tower volume, especially the larger the tower volume gets. Thus, it is not possible to assure with the necessary certainty, that the vegetable matter is uniformly distributed as it is being moved through the tower. However, for an effective leaching, it is desirable, that the ratio between vegetable matter such as sugar beet cossettes and the leaching liquid is the same throughout the volume of the tower, whereby this ratio should correspond to the technologically predetermined value which assures a most efficient leaching operation.
According to the disclosure of our above mentioned U.S. Pat. No. 3,953,224, it is possible to influence inhomogeneities occurring locally in the volume of the tower in the material passing through the tower, by adjusting the pitch angle of the guide baffles or of the wings of the conveying screws. The adjustment involves a rotational movement about the longitudinal axis of the wing or baffle and through a determined angle range. The patent also provides for controlling the quantity of material being supplied into the tower, as well as the quantity of the leaching liquid supplied into the tower. Further, our prior patent teaches to control the rotational speed of the drive shaft for the conveying screw or worm. The just described adjustments in our prior patent are performed in response to the measured values which are supplied by the pick-up or sensor to the control apparatus which in turn transforms the measured values into suitable control signals, for example, by amplification for driving a servosystem.